The present invention relates to a method of fabricating a high-integrated semiconductor device, and more specifically, to a method of forming a field effect transistor on a partially insulated semiconductor substrate.
In a system comprising a plurality of semiconductor devices, a semiconductor memory apparatus is configured to store data generated or processed therein. For example, if a request from a data processor such as a central processing unit (CPU) is received, the semiconductor memory apparatus outputs data to the data processor from unit cells therein or stores data processed by the data processor to the unit cells, according to an address transmitted with the request.
Although data storage capacity of semiconductor memory apparatus has increased, sizes of semiconductor memory apparatus have not increased proportionally. Thus, various elements and components used for read or write operations in the semiconductor memory apparatus have also reduced in size. Accordingly, components and elements unnecessarily duplicated in the semiconductor memory apparatus, such as transistors or wires, are combined or merged to reduce the area occupied by each component. Particularly, the reduction of the size of unit cells included in the semiconductor memory apparatus affects improvement of integration.
Due to the high degree of integration of semiconductor devices, the size of, for example, a field effect transistor (FET) that includes bulk silicon as the body is smaller; problems such as a short channel effect and increase of leakage current as well known to a person having an ordinary skill in the art are occurred.
In order to prevent the short channel effect and increase of leakage current, a method for fabricating a semiconductor device to form a transistor over a substrate having a silicon on insulator (SOI) structure has been suggested. The SOI substrate includes an insulating film formed over a lower semiconductor substrate and a silicon film formed over the insulating film. When a floating body transistor is formed in the SOI substrate, a body of the transistor is formed in the silicon film formed over the insulating film. The body of the neighboring transistor is isolated by a device isolation film that is contacted to the insulating film in order to reduce the leakage current. Source and drain regions are formed using both sides of the three-dimensional transistor body, thereby increasing the channel length than a conventional two-dimensional plane structure.
However, when the transistor is formed over the SOI substrate, a floating body effect is generated. The SOI substrate includes an insulating film positioned between the semiconductor substrate and the silicon film. The SOI substrate has a capacitor structure. When charges move repeatedly through the body of the transistor, the charges are accumulated in the capacitor through generation and recombination of a bias and a carrier, thereby degrading the operation of the semiconductor device. The threshold voltage of the transistor fluctuates due to the charges accumulated in the capacitor. The capacitor repeatedly accumulates and emits the charges, thereby generating thermal energy. The generation of leakage current resulting from a field effect concentration is called a Kink effect. Thus, in order to prevent degradation of the operational characteristic of the semiconductor device due to the structural characteristic of the SOI substrate, new structure for the semiconductor device is required.